A few questions which might help to find an answer...
1. What operating system are the Client machines that are having trouble connecting to OS/2 running? (I'm guessing probably Windows, but which version?)
2. Which version of OS/2 Server are you running? Warp Server 4, or OS/2 Warp Server for e-Business? Entry level or advanced? And what file system is the server running (HPFS, HPFS386, or JFS)?
3. What network protocol(s) are you using on your network (I'm guessing Netbios over TCP/IP, but I could be wrong)?
4. Which level of MPTS is installed? If you are using TCP/IP (or Netbios over TCP/IP), what level of TCP/IP stack is the OS/2 system running ? (to find out, open a command prompt window and type: INETVER)
4. What fixpaks, if any, are installed on the base OS/2 system?
5. What fixpaks, if any, are installed on the MPTS system?
6. Are there any fixpaks for the Lan Server / lan requester system installed?
There could be a few things causing the difficulty. If you can get back with the above information (especially the INETVER information - assuming you're using TCP/IP), then we may be able to figure out what's going on here.